The Third Generation Wireless Communication (3G) system utilizes CDMA (Code-Division Multiple Access) mode, supports multimedia services, and will have higher competitive ability for the coming several years. However, the 3GPP (Third Generation Partnership Project) started the research project of LTE (Long Term Evolution) for 3G wireless interface technology in order to keep this competitive ability for a longer time in the future. And AMC (Adaptive Modulation and Coding) technology has become one of key technologies of LTE.
AMC (Adaptive Modulation and Coding) technology is a physical layer link adaptation technology which can compensate the influence of fading on the signal reception due to channel variation by means of adaptively adjusting the modulation and coding mode of transmitting data, so as to improve the signal-to-noise ratio performance of the signal. AMC is realized as follows: the system establishes a Modulation and Coding Scheme (MCS) of transmission according to the physical layer ability and the channel quality, the MCS including parameters, such as the coding rate and modulation scheme for transmitting data, in which the system will choose different transmission modulation scheme and/or channel coding rate corresponding to the channel conditions to match the variable channel condition. In order to better understand the present invention, some basic technologies used in the present invention will be briefly introduced.
Currently, it is ensured that the LTE system supports two frame structures, namely a first type frame structure suitable for FDD (Frequency Division Duplex) system, and a second type frame structure suitable for TDD (Time Division Duplex) system. For better understanding of the present invention, the first and second type frame structure will be simply illustrated hereafter.
As shown in FIG. 1, it is a schematic view of the first type frame structure of FDD system in the prior art. The first type wireless frame has a length of 10 ms and consists of 20 time slots, each slot having a length of 0.5 ms, being denoted from 0 to 19. Two continuous time slots are defined as one subframe, and the subframe i consists of time slot 2i and 2i+1, wherein i=0, 1, . . . , 9.
As shown in FIG. 2, it is a schematic view of the second type frame structure of TDD system in the prior art. The second type wireless frame also has a length of 10 ms and is firstly split into two half-frames of 5 ms. Each half-frame is divided into five subframes of 1 ms. According to the specific configuration of time slot proportion, subframe 1 and subframe 6 may be configured as special service subframe and consists of three special time slots (downlink pilot DwPTS, guard interval GP and uplink pilot UpPTS). DwPTS, as well as a general downlink subframe, can be used to carry downlink service data.
In LTE (long term evolution) system, MCS is designed based on PRB (Physical Resource Block) structure of general subframe, and then AMC process is realized by means of checking TBS (transport Block Size) table. Wherein, PRB is a basic unit for resource scheduling of LTE. As shown in FIG. 3, it schematically illustrates PRB and RE in uplink time slot in the prior art, to which PRB and RE in downlink time slot is similar. Wherein, the minimum resource granularity determined by a time domain OFDM (Orthogonal Frequency Division Multiplexing) symbol and frequency domain sub-carrier is called RE (resource element). Currently, the normal PRB of a general subframe is defined as a time-frequency resource granularity with time domain of 0.5 ms and frequency domain of 180 kHz in the protocol, i.e., the time domain corresponds to 7 OFDM symbols (for normal CP) or 6 OFDM symbols (for extended CP) and the frequency domain corresponds to one time-frequency resource granularity of 12 sub-carriers.
However, in LTE system, there may be some punctured PRB resources in some special service subframe, such as DwPTS in the special service subframe of TDD system (as shown in FIG. 2), or punctured PRB owing to synchronization channel, broadcast channel etc. The punctured PRB in these special service subframes can be used to carry downlink data as a normal PRB in general subframe. However, as the existing TBS table is designed based on a normal PRB, most of which can not be directly applied to the punctured PRB.
The disadvantage of the prior art is in that: most of options are not adapted to the punctured PRB as the TBS table defined by the existing protocol is designed based on the normal PRB. If no amendment is made, then it will result in that it is impossible for the punctured PRB to choose the optimum transmission format according to channel quality, and the efficiency of spectrum transmission will be lowered.
For further understanding of the above defects in the prior art, AMC in the prior art will be briefly described as an example. However, it should be known that the hereinafter mentioned punctured PRB is only one instance in the prior art instead of representing all instances of punctured PRB in the prior art. Firstly, MCS design is implemented based on PRB structure of general subframe. For the LTE system, service channel now supports three modulation schemes of QPSK, 16QAM and 64QAM. These three modulation schemes cooperate with specific coding rate to obtain 29 MCSs, and 3 MCSs are reserved to impliedly map TBS and modulation scheme during re-transmission, thereby there are 32 options of MCS altogether, which can be indicated by 5 bits. The system selects the optimum modulation scheme and channel coding rate to transmit data according to the measurement and prediction of channel, so as to realize the maximum system throughput while ensuring a certain transmission quality. The detailed indication for MCS can be conducted with reference to the following table 1 and 2.
TABLE 1list of the modulation scheme and TBS sequence numbercorresponding to the MCS sequence numberMCS sequenceTBS sequencenumber IMCSmodulation scheme Qmnumber ITBS0201212223234245256267278289291049114101241113412144131541416415176151861619617206182161922620236212462225623266242762528626292reserved304316
Wherein, MCS indication information of 5 bits in the scheduling signalling indicates the sequence number IMCS. According to Table 1, it can be obtained the specific modulation scheme as Qm and the sequence number of TBS as ITBS. However, the specific TBS needs to be determined by ITBS in combination with the number of occupied PRB NPRB. The number of PRB NPRB can be obtained based on resource indication information of the scheduling signalling, in which the scheduling takes PRB-pair as basic granularity. After ITBS has been obtained according to table 1, it is also necessary to look up table 2 according to ITBS and the number of PRB NPRB to obtain the final TBS. The size of table 2 is 27×110, but only the portion of NPRB from 1 to 9 is illustrated for the sake of clarity.
TABLE 2TBS tableNPRBITBS12345678901632568812015217620023212448881201602002322723042327212016020024829633637634010415220827232039244050444812020026432040848855263257215223232042450460068077663201762883925046007128089367104232320472584712840968109681202483925366808089681096125691362964566167769361096125614161015232050468087210321224138415441117637658477610001192138416081800. . .122084406809041128135216081800202413232488744100012561544180020242280142645528401128141617361992228026001528060090412241544180021522472272816320632968128816081928228026002984173366961064141618002152253628563240183767761160154419922344279231123624194088401288173621522600298434963880204409041384186423442792324037524136214881000148019922472298434964008458422520106416082152266432403752426447762355211281736228028563496400845845160245841192180024082984362442644968554425616125618642536311237524392516057362664813201992266433684008458453525992
TBS table as shown in the above table 2 is designed based on normal PRB of general service, wherein in order to allow for the factors such as the system overhead for controlling the signalling and pilot as well as the extended and normal CP etc., the protocol finally assigns 120 RE downlink to each PRB-pair for carrying data, wherein 120 RE are equivalent to 10 OFDM symbols. Therefore table 2 is not suitable for the punctured PRB, particularly when more symbols are punctured. If a determination is made according to table 2, then it will lead to deviation from the actually needed MCS, and thereby resulting in decoding error of UE.
The above defect will be illustrated by the way of examples. It is assumed that UE obtains IMCS=14 and the indicated number of PRB pair is 2 according to downlink scheduling signalling. For general downlink subframe, the processing of UE is as follows: according to table 1, when IMCS=14, looking up table 1 to find the corresponding modulation scheme Qm=4, i.e., 16QAM; the sequence number corresponding to TBS ITBS=13; then according to table 2, it is found that TBS=488. Therefore, the practical code rate is generally: (488+24)/(120×4×2)=0.533, i.e., the practical MCS is {16QAM, 0.533}.
However, for DwPTS, it is assumed that DwPTS has a length of 9 OFDM symbols, then in addition to the overhead for controlling signalling, channel synchronization and pilot, the PRB in the DwPTS which can be used to carry data is approximately 5×12=60 RE. NodeB (base station) will arrange 4 PRB pairs for this UE if it is required to ensure identical transmission quality, that is, MCS needs to be {16QAM, 0.533} as well and carries 488 data bits. However, UE looks up the TBS table based on IMCS=14 and NPRB=4 which is indicated by signalling to obtain 1000 bits rather than 488 bits in fact, this will leads to error operation of UE.
Or, during scheduling NodeB considers that actually 488 bits are transmitted, then the value of TBS which is the most approximate to 488, for example 472, is selected with NPRB=4. Now the corresponding IMCS=7. When NodeB determines the transmission by means of IMCS=7 and NPRB=4, this will also result in error operation of UE as UE will be considered as MCS={QPSK, 1.06} for DwPTS, rather than MCS={16QAM, 0.533} which should be obtained. Therefore, for the punctured PRB pair in the above example, MCS {16QAM, 0.533} cannot be realized actually.